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<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
<script>
    //方式一：弹出警告框
    //window.alert("hello world");
    //方式二：写出HTML页面
    document.write("hello  js");
    //方式三：控制台输出
    console.log("hello js");
</script>    
</body>
</html>